Research efforts will be directed at understanding the mechanism of placental vitamin delivery to the human fetus: In recent years considerable progress has been made in understanding the mechanisms by which the intestine, kidney and some other body organs transport and metabolize water-soluble vitamins. However, little has been learned concerning how vitamins are delivered to the fetus by the placenta. Efforts will be directed at understanding the transfer of nicotinic acid, Riboflavin, pantothenic acid, thiamine, ascorbic acid and the product of ascorbic acid oxidation, dehydroascorbic acid. We will extend our preliminary observations which indicate that the placenta specifically recognizes at least some of these substrates. Several techniques have been selected that are expected to provide complementary information. Human placenta will be used exclusively because no animal placenta accurately models the human placenta. The latter preparation is useful in establishing whether vitamins are metabolized during placental transport as many of them are during transepithelial intestinal transport. Emphasis will be on constructing working models of vitamin delivery at the cellular and cell membrane levels. There is currently little understanding about the potential toxic effects of vitamins consumed in megadose quantities and their metabolites on the fetus. Neither has the possibility been considered seriously that defects in transport characteristics originating genetically or otherwise (e.g., alcohol) might restrict vitamin delivery and result in impaired fetal development. An understanding of normal placental function might allow future explanation of specific pathologic conditions.